﻿<p>A distribution system is a network designed to receive, store, maintain, distribute, or control the flow of a distribution media. A common example is a heating hot water system that consists of a pump, a tank, and an interconnected piping system for distributing hot water to terminals.</p>

<p>The group <em>IfcDistributionSystem</em>
defines the occurrence of a specialized system for use within the context of building services.</p>


<p>Important functionalities for the description of a distribution system are derived from existing IFC entities:</p>

<ul><li>From <em>IfcSystem</em> it inherits the ability to couple the distribution system via <em>IfcRelServicesBuildings</em> to one or more <em>IfcSpatialElement</em> subtypes as necessary.</li></ul>

<ul><li>From <em>IfcGroup</em> it inherits the inverse attribute <em>IsGroupedBy</em>, pointing to the relationship entity <em>IfcRelAssignsToGroup</em>. This allows to group distribution elements (instances of <em>IfcDistributionElement</em> subtypes), and in special cases ports directly (instances of <em>IfcDistributionPort</em>).</li></ul>

<ul><li>From <em>IfcObject</em> it inherits the inverse attribute <em>IsDecomposedBy</em> pointing to the relationship entity <em>IfcRelAggregates</em>. It provides the hierarchy between the separate (partial) distribution systems.  For example, an electrical main circuit may be aggregated into branch circuits.</li></ul>

<blockquote class="history">HISTORY&nbsp; New entity in IFC4.</blockquote>

<blockquote class="change-ifc2x4">
IFC4 CHANGE&nbsp; For electrical power systems, <em>IfcElectricalCircuit</em> has been used for low-voltage (12-1000 V) power circuits and has been replaced by <em>IfcDistributionCircuit</em> in IFC4; <em>IfcDistributionSystem</em> with PredefinedType 'ELECTRICAL' should be used for overall power systems, and <em>IfcDistributionCircuit</em> with PredefinedType 'ELECTRICAL' should be used for each switched circuit.
</blockquote>

